VB 4.2.6 a CPU hog on Win7/64bit host with no VM started

Description

Just upgraded from v4.1.22-80657 (no CPU hogging problem for this one) to the latest VB. Installed VB with both Bridging and Host-Only networking selected.
However now just starting up the new VB (with no guest VM started) my 4.2 GHz quad core 2500K pegs in at 20% for VirtualBox.exe and 28% for VBOXSVC.exe according to Task Manager.

When using Sysinternal's Process Explorer and its Thread tab for the VboxSVC.exe process we find four rather CPU consuming ntdll.dllRtlValidateHeap+0x170 threads. For process VirtualBox.exe we have two ditto named threads plus a thread called VirtualBox.exeTrustedMain+0x2bc92c.

Nothing have changed in my software setup before updating VB. And if I go back to v4.1.22-80657 there's no CPU hogging anymore...

Same issue with me.
Another effect was that log file VBoxSVC.log was getting filled with "inaccessible disk" entries. (sorry, don't have exact entry as I had to empty the file because it became VERY big).
Problem with me was a missing entry in .vbox file (automatically converted from previous version) not listing VM virtual hard disk in <HardDisks> section.

After adding the line, everything went fine.

I believe this is a bug, as I had the same configuration issue also before upgrading and did not experience any cpu hog.

Disk attachment problem should be logged only once and not continuously, as it fills disk and CPU.

UPDATE:
Just upgraded from v4.1.22 to 4.2.4 and that version is likewise working fine w/o hogging the processor whereas the 4.2.6 unfortunately has one or more coding oversights resulting in CPU overtaxing...